Compost Versus Mulch: Which to Use in Your Garden?


Compost and mulch are both useful in your garden, but they each have a specific purpose, and there is a difference between the two.

So, what is the difference between compost and mulch?  Mulch is made from wood chips, chopped leaves, straw, cardboard, or paper and used as a top layer to cover soil, retain moisture, and prevent weeds.  Compost is decomposed organic material which can be either mixed into soil to provide nutrients or used as mulch.

Both compost and mulch can be created from a variety of different materials.  Depending on the material you have available, you might be able to create your own compost or mulch.

Let’s start off with some more information about both compost and mulch, the benefits of each, when to use them, and how to find or make your own.

What is the Difference Between Compost and Mulch?

Mulch is used only as a top layer to cover soil, not worked into the soil itself.  Mulch is made of material that is not completely broken down, such as wood chips, chopped leaves, straw, cardboard, or paper.  You can usually tell what mulch is made of by looking at it – at least for a while.  Over time, mulch will break down and start to look more like ordinary topsoil.

coarse wood mulch
Mulch can be made from wood chips, but it doesn’t have to be!

On the other hand, compost is made from organic material that is already completely broken down.  When compost is “ready” for use in the garden, it looks like dark brown or black dirt, and it smells earthy, not rotten.

compost bin
When compost is “done”, it will look like dark brown or black soil, and will smell earthy.

You usually cannot tell what compost is made of by looking at it, since the materials are completely broken down and transformed into a form that plants can use for nutrition.

Compost can be worked into the soil to supplement nutrients and provide organic material for your garden.  Alternatively, compost can be spread over the top layer of soil instead of mulch.

What are the Benefits of Compost?

There are several benefits to using compost in your garden: it can help to improve nutrition, aeration, and moisture levels in soil.  As an added benefit, you can get rid of some kitchen or yard scraps if you make your own compost!

Compost Improves Soil Nutrition

Compost contains nutrients necessary for plant growth, including the “big three”: NPK, or nitrogen, phosphorus, and potassium. For more information, check out my article on the NPK ratio in fertilizers.

Compost also contains carbon, and traces of micronutrients, such as calcium, magnesium, sulfur, and others necessary for plant growth. The amount of each nutrient in your compost will depend on the materials you used.

“Green” materials, such as grass clippings or living plant material will be rich in nitrogen.  “Brown” materials, such as leaves or sawdust, will be rich in carbon.

Grass clippings and vegetable matter are good ingredients for compost.

Compost alone may not provide every nutrient that your soil needs, but it is a good start.  To make sure your soil has enough of each nutrient, along with a proper pH for your plants, it is a good idea to do a soil test.  For more information, check out my article on soil testing.

In addition to soil nutrition, compost is helpful because it provides organic material that improves soil aeration and moisture levels.

Compost Improves Soil Aeration

When you mix compost into your soil, you are exposing the soil to oxygen in the air.  The organic material in compost then helps the soil to retain more oxygen.

When soil is properly aerated, plants can absorb water properly, and beneficial microbes in the soil have enough oxygen to survive.  When soil becomes compacted (packed down), there is less air and oxygen in the soil.

Soil that is properly aerated will also allow water and nutrients to travel more easily to a plant’s roots.

Compost Improves Soil Moisture Levels

By adding compost to soil, you are adding organic material, which helps to improve soil structure, and has an effect on moisture levels.

If your soil is clay (holds water and drains poorly), adding compost will help to improve drainage.  This will help to avoid root rot, which will happen if a plant’s roots are sitting in wet soil for too long.

clay soil
Clay soil retains water and drains poorly. Adding compost can improve drainage.

If your soil is sandy (does not hold water and drains quickly), adding compost will help to improve water retention.  If you have a problem with chronically dry soil in your garden, adding compost can help to solve the problem.

Adding a layer of mulch over your soil can also help.  For more information, check out my article on dry soil.

What are the Benefits of Mulch?

Not to be outdone, mulch comes with its own benefits, such as preventing weeds, retaining moisture, and stabilizing temperature.  Mulch can also improve the appearance of your yard and garden.

Mulch Prevents Weeds

When winds blow in the spring and summer, seeds from various weeds get spread all over your yard and garden.  If they find a hospitable patch of soil, they will germinate and take root, soon crowding out and competing with the plants you want to grow.

weeds
Dandelions are a weed that spreads quickly – use mulch to keep them at bay!

Adding a layer of mulch on top of your soil prevents weed seeds from gaining a foothold.  If you already have some weeds in your garden, mulching over them will usually kill them, by denying them sunlight and air.

Mulch Retains Moisture

Mulch also helps to retain moisture in your soil by preventing rapid evaporation of water on hot, dry days.  The mulch itself can also hold moisture during heavy rains, to prevent too much water from reaching the roots of your plants.

Mulch Stabilizes Temperature

A layer of mulch over your topsoil also helps to regulate temperature, acting as a type of insulation.  This will prevent rapid swings in soil temperature, which can happen if you get a cold night in early spring (or a hot night in the fall before harvest).

When Should You Use Compost or Mulch?

If compost is completely decomposed, you can use it any time of year.  Most people work it into the soil in the spring just before planting, along with any other fertilizers or soil amendments.  You can also mix compost into your soil in the fall, and let it sit over the winter.

You can put down mulch in either fall or spring.  If you choose to lay down mulch in the spring, you may want to wait until after planting.

The reason is that you may change your mind about the location of plants at the last minute.  This is a potential problem because placing mulch too close to plants can cause them to die off (think about how mulch kills and prevents weeds from growing: in part due to a lack of air).

How to Find or Make Compost

There are several sources you can use to get compost.  One way is to go to a local garden center and buy as many bags as you need.  The only problem is that you don’t know exactly what materials were used to make the compost, or where the materials came from.

You can also go to a local compost site, usually maintained by towns and cities, to pick up some compost.  You can drop off grass clippings, leaves, and other yard waste in the summer and fall, and take compost in the spring.

Again, the only problem is that you don’t know what materials other citizens of your town dropped off at the compost site.  The compost you pick up could be made from grass that was treated with chemicals you would never use in your own yard or garden.

Compost
This compost looks fully decomposed and ready to go in the garden.

Finally, you can make your own compost yourself or with the help of friends or family.  Common materials for compost include grass clippings, leaves, straw, newspaper, cardboard, sawdust, and food scraps (fruits and vegetables – no meat or fat!)

For more information, check out my article on how to make compost.

How to Find or Make Mulch

There are a few ways to get mulch for your garden.  One way is to buy bags from a local garden center, such as Home Depot or Lowe’s.  This is probably the least cost-effective way of buying mulch, since you are not getting a bulk discount.  You also have to transport it yourself.

Another way is to order a mulch delivery from a landscaping company.  They might charge you for delivery, but you won’t have to move it yourself.  Also, you will probably end up paying less in total than you would if buying by the bag.

One last way to get mulch is to make your own.  If you want wood mulch, you can use a wood chipper, or to enlist the help of someone who owns one.  This method is the most labor-intensive, but you don’t have to pay for the mulch.

If you have trees in your yard that you want to cut down, why not turn them into mulch?  You’ll save the expense of having the trees hauled away, and you’ll save the cost of buying mulch.

One caution about mulch is that it can harbor mold growth, especially in warm, wet weather conditions. For more information, check out my article on why mulch gets moldy and how to treat it.

Finally, remember that mulch does not need to be made of wood chips.  You can use crushed cardboard boxes, paper, or straw as a layer on top of your soil to help prevent weeds from growing and to kill existing weeds. For more information, check out my article on using cardboard boxes in your garden.

cardboard boxes
Cardboard makes a good soil cover for killing and preventing weeds.

Conclusion

Compost and mulch both have their own place in the garden, and both are useful in their own way.  You should have a good idea of the benefits of each and how to go about making and using compost and mulch.

I hope this article was helpful.  If you have any questions or advice of your own about compost or mulch, please leave a comment below.

jonathon.david.madore

Hi, I'm Jonathon. I’m the gardening guy (not guru!) who is encouraging everyone to spend more time in the garden. I try to help solve common gardening problems so that you can get the best harvest every year!

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